In optical transmission equipment, transmission lines are redundantly configured to improve availability. Examples of such a redundant configuration are shown in FIGS. 1 to 3.
FIG. 1 shows an exemplary configuration of optical transmission equipment incorporating switch control of an optical transmission line to switch over between a work line and a protection line constituted on a 1:1 configuration basis. The optical transmission equipment accommodates a plurality of optical transmission lines 1, 2 . . . n in an add drop multiplexing unit (hereinafter referred to as ADM unit) 10 via corresponding interface units IF1, IF2 . . . IFn.
Each interface unit IF1, IF2 . . . IFn is provided with a pair of interface units IF1-1 and IF1-2 so as to accommodate a pair of transmission lines constituting a work line (W) and a protection line (P).
The optical transmission equipment further includes an equipment supervision and control portion 20. This equipment supervision and control portion 20 has a switchover controller 21. An alarm signal (APS) is transmitted and received to/from other optical transmission equipment through interface units IF1, IF2 . . . IFn. Equipment supervision and control portion 20 receives a switchover trigger signal SWTRG when either a line failure is detected by interface units IF1, IF2 . . . IFn or a hardware failure is detected in the transmission and reception portion of interface unit IF.
Meanwhile, in ADM unit 10, switchover units 11-1 to 11-n (which are selectors for selectively switching over from a work line to a protection line related to a certain interface unit) are provided corresponding to a plurality of optical transmission lines 1, 2 . . . n for switching work and protection lines.
Each switchover unit 11-1 to 11-n switches interface units corresponding to a work line and a protection line according to a switchover command SWCMD which is generated by switchover controller 21 based on a switchover trigger signal SWTRG from interface unit IF1, IF2 . . . IFn.
In FIG. 2, there is shown a configuration example of optical transmission equipment having built-in switchover control of work/protection optical transmission lines being provided on a 1:N basis. In this configuration example, one transmission line among a plurality (n+1) of optical transmission lines is reserved for a protection line. This protection line is switched over to work state when a failure occurs on a work line.
For this purpose, ADM unit 10 provides one switchover unit 11 (in this example, a selector to switch from a failed work interface to a protection interface), to switch the interface units corresponding to the work/protection transmission lines in response to a switchover command SWCMD sent from switchover controller 21.
FIG. 3 shows a conventional BLSR (bi-directional line switched ring) switchover configuration being allocated on a ring transmission line. Switchover controller 21 in equipment supervision and control portion 20 controls switchover unit pairs (here, circuits for either bridging or switching) 11-1, 11-2 . . . 11-n in ADM unit 10 corresponding to each plurality of transmission lines based on a switchover trigger signal SWTRG from interface units IF1, IF2 . . . IFn.
In such a conventional configuration of a redundant control system, it is essential to provide switchover controller 21 as a control unit separately provided from switchover units 11, 11-1 . . . 11-n in ADM unit 10. Therefore, it is required to prepare a space for switchover controller 21.
Also, when the number of the aforementioned switchover unit pair 11-1 to 11-n becomes larger, a control unit 21 must be divided into separate units from the viewpoint of performance, which further requires additional space.
Therefore, it is to be assumed to provide control unit 21 independently of the switchover unit corresponding to each transmission line. However, in such a configuration, normal switchover to the protection side cannot be guaranteed on occurrence of a failure in an independent control unit itself. In addition, it is necessary to evaluate a status of the protection side prior to the switchover.